Over the past decade, transgenic plants have been successfully used to express a variety of useful proteins. For example, production of proteases in plants has been achieved (See U.S. Pat. No. 6,087,558); along with production of aprotinin in plants (U.S. Pat. No. 5,824,870); and avidin (U.S. Pat. No. 5,767,379). A variety of mammalian bacterial and viral pathogen antigens are included in those proteins that have been successfully produced in plants, such as viral vaccines (U.S. Pat. No. 6,136,320), transmissible gastroenteritis and hepatitis vaccines (U.S. Pat. Nos. 5,914,123 and 6,034,298). These patents, as well as all references cited herein are incorporated herein by reference.
Many of the resulting peptides induced an immunogenic response in mice (Mason et al. (1998) Vaccine 16:13361343; Wigdorovitz et al. (1999) Virology 155:347-353), and humans (Kapusta et al. (1999) FASEB J. 13:1796-1799) comparable to that of the original pathogen. After oral delivery, these edible vaccines were immunogenic and could induce protection. Mice fed a basic diet plus corn expressing recombinant Escherichia coli heat-labile enterotoxin B-subunit (LtB) mounted a good dose dependent IgG and IgA response (Streatfield et al. “Plant based vaccines—unique advances” Vaccine (2001)19:2742-2748.) Some of the first edible vaccine technologies developed include transgenic potatoes expressing hepatitis, TGEV and Norwalk virus antigens as well as various other viral antigens. (See, e.g., Thanavala et al. (1995) Proc. Natl. Acad. Sci. U.S.A. 92:3358-3361; U.S. Pat. Nos. 6,136,320; 6,034,298; 5,914,123; 5,612,487 and 5,484,719; Mason et al., (1996) Proc. Natl. Acad. Sci. 93:5335-5340; “VP1 protein for foot-and-mouth disease” (Wigdorovitz et al (1999) Virology 255:347-353).
The utilization of transgenic plants for vaccine production has several potential benefits over traditional vaccine production methods. First, transgenic plants are usually constructed to express only a small antigenic portion of the pathogen or toxin, eliminating the possibility of infection or innate toxicity of the whole organism and reducing the potential for adverse reactions. Second, since there are no known human or animal pathogens that are able to infect plants, concerns with viral or prion contamination are eliminated. Third, immunogen production in transgenic crops relies on the same established technologies to sow, harvest, store, transport, and process the plant as those commonly used for food crops, making transgenic plants a very economical means of large-scale vaccine production. Fourth, expression of immunogens in the natural protein-storage compartments of plants maximizes stability, minimizes the need for refrigeration and keeps transportation and storage costs low. Fifth, formulation of multicomponent vaccines is possible by blending the seed of multiple transgenic plant lines into a single vaccine. Sixth, direct oral administration is possible when immunogens are expressed in commonly consumed food plants, such as grain, leading to the production of edible vaccines.
Oral vaccine delivery as the primary or booster immunization is by far the most sought after method by the aquaculture industry because it is suitable for the mass immunization of fish of all sizes, it is less stressful on fish than injection delivery, which requires handling of the fish, and because it induces mucosal immunity. However the cost-effectiveness of oral delivery has been a major barrier to commercialization of this method, especially for larger fish. Efficacy of oral antigen delivery is reported to be limited by the destruction and absorption of the antigens by the fish digestive system.
The inventors have found that transgenic plants can provide an ideal system for economical production of antigens for oral vaccination of fish.